A federal mediator has managed to — temporarily — avoid a crippling series of port closures along the East and Gulf coasts, convincing unions and employers to extend negotiations for another month beyond the expiry of current contracts on December 29.

The real good news here is that it looks like a deal has been struck regarding a central part of the dispute, the “container royalty” payments we wrote about earlier this week. The federal mediator says the dispute over the payments has been resolved “in principle”, although details of the resolution have not been made public. The director of the Federal Mediation and Conciliation Service, George H. Cohen, sounded positive in a statement:

“Given that negotiations will be continuing and consistent with the Agency’s commitment of confidentiality to the parties, FMCS shall not disclose the substance of the container royalty payment agreement. What I can report is that the agreement on this important subject represents a major positive step toward achieving an overall collective bargaining agreement. While some significant issues remain in contention, I am cautiously optimistic that they can be resolved in the upcoming 30-day extension period.”

There are still other sticking points, including over work rules and benefit changes, which means the potential for port closures remains a real one — just with a deadline toward the end of January, rather than December.

So while some are relieved at today’s news, those with the most at stake will still be watching this situation closely for resolution before the new deadline. What exactly is at stake? Here’s what the WSJ’s Betsy Morris tells us:

The big box retailers – Walmart, Target Home Depot, Lowe’s and Sears – are among those likely to be most affected by a dockworker strike at ports along the East and Gulf coasts, says Scott Group, transportation and logistics analyst at Wolfe Trahan. The auto industry could also be hurt, he says, because some parts and components travel via ocean containers; their supply chains are so tightly wound that if a part doesn’t arrive on time, it can halt manufacturing of a particular car model. “Their supply chains can get disrupted very quickly,” he says. “If they don’t get the parts for production of a car when they need them, they may need to shut down manufacturing of that car.”

If there is a strike, he estimates it would last about a week, based on past history. The 2002 lockout lasted about ten days, he says; the recent strike at the Ports of Los Angeles/Long Beach by the clerical workers lasted eight days. He does not think President Obama would be quick to impose Taft-Hartley, since the action wasn’t taken last month in the West Coast strike.